The "Flameproof Enclosure" ignition protection type is a type of ignition protection, in which electric operating equipment and other appliances are accommodated in a closed housing. The housing must satisfy specific test conditions. It is necessary, inter alia, to ensure that, if an ignitable gas mixture ignites in the housing, no particles and no hot gases can escape outward which may possibly ignite the atmosphere in the vicinity of the housing, if an ignitable gas mixture is also present there. This condition relating to the retention of ignitable particles and hot gases can be achieved if the cover of the housing forms with the housing a so-called "ex-gap". During passage through the "ex-gap", the particles and gases are sufficiently cooled to be no longer capable of causing any damage outside the housing.
So that the "ex-gap" can perform its function, it must be sufficiently narrow and long, and the gap width should under no circumstances increase over time. In this case, in particular, the gap width is an essential criterion which, where large volumes are concerned, has hitherto been possible to adhere to sufficiently only by means of housings manufactured from metal. Housings injection-molded from plastic present the problem that the housing dimensions in the region of the parting plane between lower part and upper part of the housing and cover are subject to such pronounced material-related and process-related tolerances that it has not been possible to satisfy the conditions for an "ex-gap" there.
It has therefore been necessary hitherto, in the case of housings produced from plastic, to ensure the "Flameproof Enclosure" ignition protection type by connecting upper part and lower part of the housing integrally to one another at the parting plane by means of a sealing compound. However, the housing is consequently closed permanently and the electric operating equipment inside the housing can be reached only when the housing is destroyed.